Method of making spark plugs



R. T. HURLEY METHOD OF MAKING SPARK PLUGS July 21, 1931.

Original Filed March 13, 1930 Zvl/IIIIIIIVWIIIIIIWI/Ill Patented July 21 1 931 g UNlTED I STATES PATENT v OFFICE ROY '1. HUBLEY, OF DOBBS FERRY, NEW YORK, ASSIGNOR TO HURLEY-TOWNSEND COB PORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE METHOD or mm; srARx raves Original application filed larch 13, 1930, Serial No. 435,461. Divided and this application filed March 7,

' 1931. Serial No. 520,948.

This invention relates to a method of making spark plugs, and has for an important object to contrive a practical, eflicient and economical method for constructing a spark plug 5 which will be well sealed at all times against the escape of gases through. it, and which will be well adapted to avoid overheating even under the exacting conditions imposed in heavy duty engines such as thoseemployed in ther objects and advantages will hereinafter appear.

The present application is a division of my pending application, Serial No. 435,461,"filed March 13, 1930.

In the drawings forming part of this specification, F

Figure 1 is a vertical sectional view taken centrally through a spark plug made in accordance with the method of the present invention;

Figure 2 is a vertical, sectional, detail view through an expansible sleeve employed in the spark plug of Figure 1 F lgure 3 is a plan view of the sleeve of Figure 2; 1

Figure 4 is a sectional view taken on the line 44 of Figure 2, looking in the direction of the arrows; and

Figure 5 is a vertical sectional view through a modified form of expansible sleeve which may be employed showing the expanding ball and upper end of the electrode inserted within the lower end of the tube in position for" expanding the same, but omitting the insulation and retaining member which are assembled on the sleeve before the expansion operation is carried out.

The illustrative spark plug comprises an externally threaded shell 1 adapted to be threaded into a motor. The shell 1 carriesa spark electrode 2 which forms one terminal of the spark gap. An insulatorand central electrode assembly 3 comprises-an externally threaded nut 4 which is screwed tightly into the shell 1 to co-act with the shell in firmly clamping an interposed gasket 5 to form a tight seal. The nut 4 serves as a. retaining and supporting member for the central assembly 3.

The central assembly 3 also comprises an expanded. sleeve 6, (see Figures 2 and 3) of v malleable metal preferably having high heat provided with the flange 7, but before the steps of incorporating it in a spark plug are begun, longitudinall extendinv oves 8 are formed in the out r face of tlie t l b e. The grooves 8 terminate a short distance above the lower end of the sleeve. Since the formation of thegrooves displaces some of the metal inward, the outside diameter of that length of the sleeve in which the grooves have been formed is reduced by the formation of the grooves and is less than that of the ungrooved lower end portion.

A sheet of compressible, heat-resisting, in-

sulating material, such as mica, is tightly wrapped into a multiple-ply tube 9 which surrounds the sleeve'6. Upon this tube 9 the lower end 10 of the insulator is built up of washers of suitable insulating material, such as mica. The nut 4 is then impaled upon the tube and the upper end 11 of the insulator is built up by placing upon the tube further washers of mica or other suitable material. As thus assembled, the nut 4 does not bind upon the tube 9 but fits it rather snugly.

The central electrode -is next inserted in the sleeve 6 from the lower end thereof, The

central electrode comprises a shank 12 and a nose 13, the nose being larger than the shank, but of such small mass that the heat absorbed by it may be rapidlyv and efficiently conducted engine. The nose l3 carries a sparking tip 14 of suitable material, such as nickle-manganese wire.

Prior to the insertion of the central'electrode, the sleeve, insulator and nut assemblyis longitudinally compressed, and this pres-v sure is maintained throughout the insertion of the electrode.

The shank 12 of the central electrode is of a diameter to snugly fit within the ungrooved lower end of the sleeve. 6. It may be started in the sleeve readily therefore, but when it reaches the internal ribs formed by grooving of the exterior of the sleeve, it must be driven. This driving of the electrode through the'sleeve eliminates the grooves and expands the grooved portion of the sleeve to the diameter of the ungrooved portion. Such expansion of the sleeve 6 simultaneously applies circumferential tension and radial pressure to the tube wall 9 so that the tube wall is pressed with considerable force between the sleeve and the nut 4. The shank 12 and the sleeve 6 have at least as high coefficients of heat-expansion as the nut 4, so that this pressure is not relieved when the spark plug becomes heated in use.

After the insertion of the central electrode, the conductive terminal 15 is placed upon the upper end of the shank 12 and the upper end of the shank is upset, as shown at 16, to hold the parts in assembled relation and under pressure. The described construction is efficient under all operating conditions and is especially eflicient under heavy duty conditions of operation because the central electrode 'does not tend to overheat and cause pre-ignition. As has been stated, the shank 12 of the central electrode is relied on lar ely for conducting away the heat absorbe by the electrode nose 13. In order that the shank may perform this function, efficiently, it is important that the shank be protected against the circulation of hot gases around it, since the absorption of heat by the shank from any source other than the electrode nose will necessarily reduce the temperature gradient of the shank. It is of especial importance that the circulation of gases between the shank and the nut be avoided because the mass of metal forming the nut serves as an effective means of withdrawing heat from the shank at the point where the insulation is of minimum thickness. The described construction is effective to maintain the shank and sleeve in as intimate heat-transferring relationship with the nut 4 as is consistent with maintaining good electrical insulation between the shank and the nut.

Figure 5 illustrates a modified form of carrying out the process. The essential difference between this method and the one described hereinabove resides in the expansion of the copper-like sleeve by means and devices other than the electrode, thereby prearing a substantially completed supportor the electrode, this support comprising the nut, the insulation tubeand the cop-per or copper-like tube properly expanded to compress the insulation to form the rigid and leak proof unit. The electrodeis then forced into this unit to obtain a close fit. More particularly in this modified form of the invention a cylindrical sleeve 6A is expanded by expanding the tube, which is shown as having its lower portion relatively enlarged, with reference to the remaining portion 17. It' will be understood that, as in the method described hereinabove with reference to the form shown in Figure 2, the copper or copper-like sleeve 6A is assembled with the mica sleeve 9, nut 4 and the mica washers 10 and 11, prior to the expansion step, the washers and nut being held under endwise compression during the expansion.

While I have illustrated and described in detail certain preferred methods of carrying out my invention, it is to be understood that changes ma be made thereinfalling within the scope o the appended claims. I do not, therefore, desire to limit myself to the specific methods illustrated or described, but intend to cover my invention broadly in whatever form its principle may be utilized.

I claim:

1. The method of making a spark plug adapted for heavyduty work ,where it is subjected to high temperature and pressure conditions and severe vibrations, including the provision of a rigid body having a smooth bore, introducing therein a relatively yieldable tubular insulating, member and a copper-like sleeve disposed interiorly of said member, said insulating member and sleeve extending exteriorly of said bore, assembling mica-like washers on said extended portion, and forcibly expanding said sleeve throughout said bore to an extent suflicient to efiect a coextensive rigid clamping and sealing of the insulating member between the rigid body and the expanded sleeve.

2. The method of making a spark plug adapted for heavy duty work where it is subjected to high temperature and pressure conditions and severe vibrations, including the provision of a rigid body having a smooth centrally disposed bore, introducing v therein a relatively yieldable tubular insulating member and a malleable metal sleeve disposed interiorly of said member, said insulatingmemberand sleeve extending exteriorly of said bore, and forcibly expanding said sleeve throughout said bore to an' extent suflicient to eifect a coextensive rigid clamping and sealing of the insulating member between the rigid body and the expanded sleeve. w

3. The method of making a spark plug for heavy duty work including the provision of a metallic body portion having a centrally disposed bore, introducing therein a relatively yieldable insulating member and a copper-like sleeve disposed interiorly of said member, forcibly expanding said sleeve throughout a substantial length of said bor and to a suflicient extent to effect a coextensive clamping of the insulating member between the metallic body portion and the expanded sleeve with sufficient pressure to seal the respective contacts between said body portion, insulating member and the sleeve against leakage of gas pressure underheavy duty service and to convert said elements into a unitary rigid assembly, and fitting an electrode tightly in said sleeve.

4. In the art of manufacturing spark plu s, the steps which consist in providing a tu e of mica-like insulating material, assembling on said tube a spark plug body portion having a bore therein snugly fitting the tube, assembling a plurality of mica-like insulating washers on said tube at each side of said body portion, subjecting said assembled washers and body portion to end-wise compression, and expanding said tube into sealing engagement with the walls of the sald bore throughout a substantial length there-v of, the inner surface of said tube being protected against rupture during said expansion.

5. The method of making a spark plug adapted for heavy duty work where it is subj acted to high temperature and pressure conditions and severe vibrations, including the provision of a rigid body having a smooth bore, introducing therein ,a relatively yieldable tubular insulating member faced exteriorly by a copper-like sleeve, said insulating member and sleeve extending exteriorly of said bore, assembling mica-like washers on said extended portion, driving through the sleeve an expanding member having substantially circumferential line contact with the sleeve to expand the same and effect a coextensive rigid clamping and sealing of the insulating member between the rigid body and the expanded sleeve.

6. The method of-making a spark plug adapted for heavy duty work where it is subj ected to high temperature and pressure conditions and severe vibrations, including the provision of a rigid body having a bore, introducing therein a relatively yieldable tubular insulating member and an interiorly disposed copper-like sleeve, said'sleeve having one or more longitudinal corrugations, said insulating member and sleeve extending exteriorly of said bore, assembling mica-like washers on said extended portion, and forcibly expanding said corrugations to eflect a rigid clamping and leak-proof-sealing of the insulating member between the rigid body and the sleeve. I

7. The method of making a spark plug adapted for heavy duty work where it is subjected to high temperature and pressure conditions and severe vibrations, including the rovision of a rigid body having a smooth ore, introducing therein a relativel yieldable tubular insulating member and an interiorly disposed copper-like sleeve, said sleeve having one or more lon 'tudinal cdrrugations, said insulating mem er and sleeve extending exteriorly of said bore and forcibly expanding said corrugations to effect a rigid clamping and leak-proof sealing of the insulating member between the rigid body and the sleeve, by forcibly introducing a spark plug electrode thereinto, such introduction of the electrode also effecting a leak-proof seal between the inner wall of the sleeve and the surface of the electrode.

8. The method of making a spark plug which comprises forming a rigid body member with a central bore, introducing therein in snug fitting relation a tubular insulating member and a metallic sleeve disposed interiorly of said insulating member, said insulating member and sleeve extending exteriorly of said bore, assembling insulating elements on said extending portion, driving through said sleeve in advance of an electrode, an expanding member having a rounded sleeve-engaging surface to expand the sleeve and effect a gas-tight joint between said sleeve and said insulating member and between said insulating member and said body member.

9. The method of making a spark plug which comprises forming a rigid body member with a central bore, introducing therein a tubular insulating member and a metallic sleeve disposed interiorly of said insulating member, said insulating member and sleeve extending exteriorly of said bore, assembling insulating elements on said extending portion, driving through said sleeve an expanding member having a substantially spherical surface, the diameter of which is greater than the inside diameter of said 

